The correct answer is C. Comma
Step-by-step explanation:
In grammar, the comma which is a punctuation mark introduces a pause between elements in a sentence or paragraph in different ways. Indeed. the comma has multiple functions that include separating different elements or items in a list, address, long numbers or dates; linking two independent clauses if these include connectors such as and, or, but and marking introductory words or phrases which are elements that appear at the beginning of the sentence and serve as a context such as the introductory phrase "After exercising" in the sentence "After exercising, you need to drink water". In this way, the comma shows the end of the introductory phrase and the beginning of the main sentence. Thus, the punctuation mark that is required to set apart an introductory phrase is a comma.